Soil acidification has been of concern in the oil sands region in Alberta due to increased acid deposition. Using the canopy budget model, and accounting for H(+) canopy leaching by organic acids, we determined sources and sinks of H+ in throughfall in jack pine (Pinus banksiana) and trembling aspen (Populus tremuloides) stands in two watersheds from 2006 to 2009. In pine stands, H+ deposition was greater in throughfall than in bulk precipitation while the opposite was true in aspen stands. The annual H+ interception deposition was 148.8-193.8 and 49.7-70.0 molcha(-1) in pine and aspen stands, respectively; while the annual H+ canopy leaching was 127.1-128.7 and 0.0-6.0 molcha(-1), respectively. The greater H+ supply in pine stands was caused by greater interception deposition of SO4(2-) and organic acids released from the pine canopy. Such findings have significant implications for establishing critical loads for various ecosystems in the oil sands region.